1. Field
The present teachings relate to VSWR (voltage standing wave ratio) detection. More particularly, the present teachings relate to VSWR detection using a replica circuit.
2. Description of Related Art
VSWR (voltage standing wave ratio) is a metric commonly used to indicate a degree of impedance mismatch between two different stages in a circuit (e.g. a power amplifier and a transmitting antenna). A VSWR of 1:1 indicates a perfect impedance match (e.g. no reflected wave) while higher measures of VSWR indicate higher degrees of impedance mismatch (e.g. a VSWR of 10:1 indicates higher impedance mismatch than a VSWR of 5:1). In prior art embodiments, measurement of VSWR can be performed using a dual directional coupler and a complete power detector in order to measure both forward and reflected waves from which the VSWR measurement can be derived.
For example, an impedance mismatch between two stages of a circuit such as a power amplifier and a transmitting antenna can occur because antenna impedance can be influenced by a surrounding environment of the transmitting antenna. By way of example, and not of limitation, at assembly time the antenna may have a particular surrounding environment, leading to a first value of antenna impedance. The power amplifier may be matched to the first value of the antenna impedance. If the environment surrounding the antenna changes, antenna impedance may change to a second value as a result of the environmental change. As one example, placing the transmitting antenna on a metal table can alter the antenna impedance, causing an impedance mismatch between the power amplifier and the transmitting antenna. As another example, metal objects in proximity to the transmitting antenna can affect the antenna impedance.